The present invention relates to an encapsulated, waterproof temperature sensor, and in particular to a thermistor for use with water beds.
Water beds have become increasingly popular in recent years. It is usually desirable for the water within the bed to be heated so that body heat from the user is not lost to the water and so that the bed does not feel cold. Water bed heaters are now commonly employed. Thermistors have been used to monitor water bed temperature. A thermistor is a resistor, the resistance of which is predictably varied according to temperature. Resulting variations in electric current through the thermistor can be analyzed by known means to determine the temperature of a particular environment, such as a water bed. The information provided by the thermistor may be conveyed to a control device to regulate the water bed heater and thus the bed temperature so as to maintain the latter at an optimal level.
Normally, thermistors do not contact the water in the water bed. It is common to extend a cord through a water bed frame to a thermistor disposed against the base of the water sack. Accordingly, under normal conditions, it has not been necessary to provide submersion safe thermistors or thermistor cords.
However, safety considerations dictate that a user be protected from electrical hazards in the event of a leak in the water bed. Accordingly, certifying agencies such as Underwriters' Laboratories, Inc. and the Canadian Standards Association have developed safety standards for thermistors that are used with water beds. The standards require that the water in which a thermistor is immersed remain effectively electrically insulated when 3000 volts is applied between the cable conductors and the water, which is grounded.
Accordingly, it is an object of the present invention to provide an improved temperature sensitive device, such as an encapsulated, waterproof thermistor, which can surpass the above standard. Of course, the thermistor should perform its usual function in an exemplary fashion. A further object of this invention is to provide an economical and reliable method of manufacturing such device.